Scanning antenna



Jan. 23, 1962 K. c. KELLY 3,0 8, 7

SCANNING ANTENNA Filed Feb. 2, 1959 4 Sheets-Sheet 1 Jan. 23, 1962 K. c. KELLY 3,018,479

SCANNING ANTENNA Filed Feb. 2. 1959 4 Sheets-$heet 2 IAAM Jan. 23, 1962 K. c. KELLY 3,018,479

SCANNING ANTENNA Filed Feb. 2, 1959 4 Sheets-Sheet 3 4rraw af Jan. 23, 1962 K. c. KELLY SCANNING ANTENNA 4 Sheets-Sheet 4 Filed Feb. 2, 1959 y; M 5 a V/ I W 7 a 54 4 I m A N W a United States Patent Office 3,018,479 Patented Jan. 23, 1962 3,018,479 SCANNING ANTENNA Kenneth C. Kelly, Gardena, Calif., assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Filed Feb. 2, 1959, Ser. No. 790,765 12 Claims. (Cl. 343-762) This invention relates to scanning antennas, and particularly to streamlined scanning antennas which operate in the microwave region and whichcan be used in aircraft and other high speed vehicles.

For many applications, particularly high speed aircraft, it has been difficult to provide an antenna which can scan in a forward direction but which does not introduce excessive weight or aerodynamic problems. With high speed aircraft, for example, it has usually been the practice to utilize a point source of energy and a reflector and to provide the desired streamlining by utilizing a radome of hemispherical or conical shape. When this is done, the nose area of the aircraft is not eificiently utilized because no structure can be placed in the space between the refiector and the radome. Furthermore, the reflector often requires a heavy and complicated rotating structure and the radome introduced errors in the radiation characteristics of the antenna. Where the radome is modified to improve the radiation characteristics, the resultant structure is usually not sufficiently strong to withstand the tremendous pressures and forces existing in high speed operation.

It has therefore been found desirable to construct antennas which conform to the conical configuration of the nose of an aircraft. When this is done with the devices heretofore available, however, scanning could not be provided without the use of a structure which had undesirable combinations of weight, volume and radiation characteristics.

It is therefore an object of the present invention to provide an improved scanning antenna which is capable of providing an aerodynamic surface for a forward part of a high speed aircraft.

Another object of this invention is to provide a microwave scanning antenna which is lighter in weight, more simply driven and which occupies less volume than the devices heretofore available.

A further object of this invention is to provide an improved streamlined microwave antenna which can provide a scanning beamof selected polarization characteris' tics.

Yet another object of this invention is to provide an improved antenna which simply yet effectively provides scanning of a given region in space.

These and other objects are achieved by an arrangement which utilizes a conical transmission line consisting of outer and inner conductive cones. The outer cone may provide the nose structure of an aircraft or other high speed vehicle, and includes radiating apertures in its surface. The apex of the outer surface of the inner cone is geometrically common with that of the inner surface of the outer cone, but the inner cone is mounted so as to be angularly movable with respect to the central axis of the outer cone. As the inner cone is shifted with respect to the outer of the two cones, different longitudinal segments from the apex to the base, are placed in close proximity. The conical transmission line is excited from a central feed extending from the interior of the inner cone to the apex of the two cones. A multiplicity of small radiating slots or holes through the outer cone are so placed to cause waves emanating from each one to reinforce in the forward direction. Thus collimation of a beam is achieved. Scanning of the beam is achieved by utilizing dielectric elements in the space between the outer and inner cones. The dielectric elements slow the wave energy to an extent dependent upon the dielectric constant of the dielectric and the size of the air gap between the two dielectric cones. The relationship between the velocity of the propagated wave and the disposition of the apertures is selected so that a single reverse end fire beam in space is directed forward from the apex of the assembly. As the inner cone axis is displaced with respect to the outer cone axis, keeping the above-mentioned apexes together, the direction in which the beam collimation takes place also changes. The beam may be caused to scan to an angle many times the angle of the inner cone displacement angle by choice of dielectric materials and dimensions.

The novel features of this invention, as well as the invention itself, both as to its organization and method of operation, may better be understood When considered in the light of the following description, taken in conjunction with the accompanying drawings, in which like reference numerals refer to like parts, and in which:

FIG. 1 is a simplified perspective representation of a scanning antenna in accordance with the present invention mounted in a forward end of a high speed aircraft;

FIG. 2 is a side sectional view of a scanning antenna in accordance with the present invention;

FIG. 3 is an end view of the antenna of FIG. 2, partially broken away, showing a portion of the distribution of radiating apertures therein;

FIG. 4 is a simplified fragmentary view of a portion of a conical transmission line as employed in the present arrangement, and which is useful in explaining the relationship between the disposition of the apertures and the confined wave energy;

FIG. 5 is a simplified representation of a scanning antenna in various positions of operation, showing the mantion may be mounted on the nose of a high speed air-' craft, such as the jet aircraft 10 shown in simplified fashion. The scanning antenna 20 may consist of a streamlined cone mounted on the nose of the aircraft 10. The cone may include radiating apertures 22, indicated only generally, in the outer surface thereof, various arrangements for which are discussed in more detail below. It is intended with this arrangement to provide a scanning beam about the longitudinal axis of the scanning antenna 20 and the jet aircraft 10-. The beam patterns indicate-d by solid and dotted lines in FIG. 1 are of course'greatly simplified and merely used to illustrate the various positions occupied by the radiation pattern as the beam scans. The angle at which the beam may scan from the axis depends on the design of the antenna 20 as does the shape of the radiation pattern.

The arrangement of the scanning antenna of FIG. 1 may be better understood by reference to the side sectional view of FIG. 2 and the end view of FIG. 3, in which only a portion of the antenna 20 surface is shown in detail. As may best be seen in FIG. 2, the scanning antenna 20 includes an outer conical conductive section 24 symmetrically disposed with respect to a longitudinal axis and having an apex 25 on the axis. The ape-x 25 of the outer cOne or shell 24 may, of course, provide a leading edge for the fuselage of the jet aircraft 10 of FIG. 1. The angle defined by the sides of the outer cone 24 from the apex 25 may be selected to conform aerodynamically to the associated surfaces of the jet aircraft 10. In conjunction with the outer cone 24, a conical transmission line for microwave energy may be provided through the use of an inner conductive cone or shell 26 having a geometrical apex 27 which is replaced by the tip of the center conductor 32 of a coaxial line 30. The inner conductive cone 26 has a smaller apex angle than the outer cone 24. The apexes and 27 of the two cones, 24 and 26 re spectively, are thus coincident. The outer cone 24 may be covered by a thin dielectric cover 29 which is substantially transparent to microwave energy.

Microwave energy for feeding the conical transmission line is derived from an inner coaxial line 30 having an outer conductor 31 extending through a registering aperture near the apex of the inner cone 26, and a center conductor 32 forming a pivot at the apex 25 of the outer cone 24. At least a portion of the coaxial line 30 may be sufficiently flexible to move with the remainder of the structure. Input energy is provided from an input coaxial line 50.

The cortical transmission line formed by the outer cone 24 and the inner cone 26 is terminated at its base in a resistive termination band or disk 36 fixed to the outer cone 24. Thus energy in the dominant mode of the conical transmission line is propagated in three-dimensional fashion as a traveling wave from the apex to the termination 36 at the base. The energy radially expands from the central axis as it moves from the apex to the base. A slow wave operation is achieved as to this transmitted energy through the use of a pair of inner dielectric members 40 and 42 in the form of hollow circular cones. The first dielectric cone 40 is disposed inside and in registry with the inner surface of the outer conductive cone 24. In many structures, it may be desired to utilize this first dielectric cone 40 as a support on which to place the relatively thin outer conductive cone 24. This is particularly true if the apertures 22 of the outer cone 24 are to be narrow circular slits and not elongated slots. The first dielectric cone 40 is symmetrical with the axis of the outer cone 24 and uniformly increases in thickness in the direction proceeding from the apex to the antenna base. The second dielectric cone 42 is similarly disposed on the outer surface of the inner cone 26. When the dielectric cones 40 and 42 are concentric a gap exists between them along the antenna structure.

Dielectric material which may be used for the first and second cone 40 and 42 may be any of a number of low loss materials for efficiency of operation, such as polystyrene or polytetrafiuoroethylene. The dielectric constant of this material, which affects the speed of energy propagation therein, is related both to the spacing of the apertures 22 in the outer cone 24 and to the spacing between the outside of the second dielectric cone 42 and the inside of the first dielectric cone 40, and to the maximum scan angle desired. As is described in more detail below. the speed of propagation of a wave transmitted alon the conical transmission line varies with t e eircum ferential position about the conical transmission line when the axis of inner cone 26 is displaced with respect to that of outer cone 24.

Movement of the inner structure, consisting of the inner conductive cone 26 and the second dielectric cone 4-2, may be accomplished by a positioning mechanism 43 coupled through a fixed arm 44 to a support ring 45 inside and attached to the inner cone 26. The mechanical positioning mechanism 42 is shown only generally, because it may be any driven or manual device for angularly shifting the position of the inner structure with respect to the outer. The relative directions of movement possible in this plane are indicated generally by arrows.

The manner in which the radiating apertures 22 are spaced about the outer conductive cone 24 may be seen in FIG. 3. Elongated slots 22 which are cut into the outer cone 24 may be employed, in an arrangement having the appearance of that shown in FIG. 3. In FIG. 3 may also be seen the use of the outer layer 29 which is transparent to microwave energy and which provides a completely uniform and smooth structure. In accordance with known antenna synthesis techniques, the disposition of the slots 22 between the apex and the base of the antenna 20, and their circumferential position about the outer cone 24, may be varied to achieve a desired beam pattern and characteristics. In particular, to achieve a pencil beam the slots on one half of cone 24 are displaced from slots on the other side by d/ 2 when the confined waves in the region between cones 24 and 26 are traveling in a TEM like mode.

In operation, the arrangement of FIGS. 2 and 3 pro vides the desired scanning operation as wave energy provided from the input line 50 is transmitted within the conical transmission line. In this operation, the movement of the inner assembly with respect to the outer assembly may of course be incremental or may be moved between separate positions in a programmed or other fashion, depending upon the directions which are to be scanned with the beam. It should be noted that for purposes of reference the term angular is here employed in conjunction with pivotting movements about the apex 25, and the terms rotational or circumferential are employed in conjunction with rotary positions or move ments about the axis of the structure.

Energy in the dominant TEM mode of a coaxial line is fed from the input line 30 to the point between the real apex 25 and the geometric apex 27 of the inner and outer cones 26 and 24. The center coaxial line 30 establishes a distorted dominant conical transmission mode between the inner and outer conductive cones 24 and 26, the wave energy terminating at the resistive termination 36 of the conical transmission line. Without the use of the dielectric cones 40 and 4-2 and the other features of the invention, the wave propagated in the conical transmission line mode would be a fast wave which could not provide a beam pattern in the desired forward direction without also creating other unwanted beams. The presence of the dielectric cones 40 and 42, however, and of the intervening space, slows the wave to an extent approximately determined by the relative volume filled by dielectric and the intervening gap, and square root of the dielectric constant of the dielectric cones 40 and 42.

What the present arrangement makes possible, therefore, is the control of propagation speed along the conical transmission line in the direction from apex to base, and the variation of this speed circumferentially around the conical transmission line.

As the inner assembly, including the inner cone L6, moves, a zero gap between the two cones 24- and 26 is present along one selected line from the apex to the base. The velocity of the wave will be slowest at the minimum gap and the contributions from the aperture along and around that line will contribute to a beam pointed at a large angle with respect to the axis of the outer conductive cone 24. On the opposite side of cone 24 there will be a line where the air gap will be a maximum at the same time. The apertures 22 on this side will be excited by a wave which will have the fastest velocity encountered and these apertures will also contribute to the above-mentioned beam direction since they are on an opposite side. The arrangement thus makes possible the generation of a reverse end-fire beam at a direction determined by the relative positions of the central axes of the inner cone 26 and the outer cone 24.

The advantages of this arrangement and further modifications which may be made will now be apparent. The shifting of the relative axial positions of the two cones 24 and 26 may be provided by a number of structures within the concept of the positioning device shown gen erally by way of illustration. The inner and outer cones 26 and 24 may have any relative thicknesses desired, and particularly the outer cone 24 may consist of a. thin conductor which is physically maintained and supported by the associated dielectric cone 40. To provide a completely flush surface, the apertures 22 in the outer cone 24 5 may be filled, or the entire structure may be covered, with a material 29 which is substantially transparent to microwave energy, but which would have metal support behind which also is a heat sink to conduct away aerodynamically produced heat.

The device thus provided is simple to construct but has the desired aerodynamic properties. It is nonetheless light in weight and occupies relatively little volume, because the interior of the inner cone is free of transmitted energy and may be utilized for other purposes. Although the device has been described only in the transmitting mode, it is of course to be recognized that the reciprocal nature of antennas permits a corresponding operation when receiving energy.

Although considerations as to the synthesis of the antenna aperture should be apparent to those skilled in the art, some further discussion Will be provided in order to make the relationships fully clear. Reference may be made to FIG. 4, which shows an arrangement generally like that of the previous figures. The arrangement is slightly different in the use of the dielectric members, however, because in FIG. 4 only a single dielectnic cone 41 bonded to the inner conductive cone 26 is provided. Thus the reduction in the velocity of the propagated wave is provided by the single dielectric cylinder 41, and the variation in this velocity is provided by the dielectric cylinder 41 in combination with the gap between the cylinder 41 and the outer cone 24.

The wavelength of energy in free space will be called A and the wavelength of the wave in the conical transmission line Will be termed A As shown in FIG. 4, the spacing between the apex 25 of the outer cone 24 and the first half circle of apertures on one side is given the distance a, and the spacing between the apex Z5 and the corresponding apertures on the other side of the cone is given the distance b. The distances a and b are selected so as to provide linear polarization by making a-l-d/2=b. The distance d is determined by the angle occupied by dielectric cone 41, or dielectric cones 40 and 42, and the angle of the air gap. The principal consideration here is the provision of the desired single forward scanning beam through use of a reverse end-fire radiation.

The same considerations apply as to the provision of the desired beam, whether the antenna aperture consists of elongated slots 22, as shown, or separate half rings, or a continuous spiral of pitch d which would achieve circular polarization. To achieve the desired single beam, the spacing d between successive aperture elements in the direction from apex to base must be selected with respect to the other controllable parameters. For a traveling wave taken in the direction shown (from apex to base), and considering the situation at one line on the conical surface of cone 24, an angle 6 representing the angle of point in real space as shown in FIG. 4, the beam maximums are given by the relation where m is any coexisting integer 0, 1, 2, 3, 4, 5 etc. This equation signifies that for beam maximums to be in real space the value of the bracketed quantity must be somewhere between plus and minus unity for some values of m. To provide the desired single beam, therefore, the bracketed quantity must have this value for only one value of m. When this result is accomplished, second order beams are in nonexistent space.

The present invention makes possible the achievement of the result through the inter-relation of the wavelength of the slow wave and the spacing of the successive apertures. The use of the slow wave means that Hence by making d correct, only one value of m will provide a quantity within the brackets which is between plus and minus unity. One and only onebeam in real space is provided when this relation has been followed in the present structure.

The manner in which different beam directions may result is illustrated in the simplified representation of FIG. 5. As there shown, a concentric relationship between the two conductive cones 24, 26 and the dielectric structure 41 results in an on-axis beam. An angular movement of the inner cone 26 about the apex and relative to the outer cone 24 causes a corresponding movement of the beam. Beam movement is proportional to the extent of relative movement of the two cones 24, 25. Consequently, there can be provided a scanning pattern which is in the form of a rectangular raster, which is directed only at specific points, or which has some other form. In devices constructed in accordance with this invention it has been found that a beam can be directed 15 degrees oi]? the central axis by a relative movement of only 3 degrees of the two conductive cones 24, 26.

A different arrangement of an antenna in accordance with the invention is shown in FIG. 6,, to which reference is now made. In this exploded view, an outer conductive cone 24 similar to that previously described is employed, the cone having radiating slots 22 spaced in its surface. Here again, for a linearly polarized pencil beam, these slots 22' are disposed on half circles concentric with the axis of the outer cone and spaced along the outer cone 24' in alternating fashion. The inner structure 52 consists in this arrangement of an inner cone 53 covered by a dielectric layer 41 in the fashion of the arrangement of FIG. 5. The center conductor 32 of the coaxial line extends through the tip of the inner structure 52 to contact the inner apex of the outer cone 24'. The desired termination for microwave energy provided in the conical transmission line mode is achieved through the use of a plurality of resistive vanes 55 positioned at the base of the structure. To accommodate these vanes 55, the inner structure 52 at its base portion is tapered oppositely to the remainder of the inner structure 52.

The operation of this antenna follows the general form previously described. The inner structure 52 may be moved angularly by positioning means (not shown in this figure) with respect to the outer cone 24', and as the inner structure 52 is moved selected slow wave propagation results, causing a reverse end-fire beam in a selected direction in space. The resistive vanes 55 parallel to the direction of propagation of the dominant conical transmission line mode attenuate the energy to provide a traveling wave operation.

A conical scanning antenna may also be providedin accordance with the invention, as shown in FIG. 7. As illustrated therein, the conical scanning antenna may include an outer cone 24 and an inner cone 26", with an interposed dielectric structure 41" corresponding to the like elements of the arrangements above described. With this structure there may be included means by which the inner structure is rotatable or circumferentially movable in the desired fashion with respect to the aircraft and the outer cone. Only one of the driving mechanisms which might be used is shown. A circumferential scan in space is provided by a continuously rotating drive motor (not shown) may be coupled by a belt 56 and a pulley 57 to the inner structure. The pulley 57 may be mounted on the coaxial waveguide 30, the center conductor 32 of which may act as a pivot point at the apex of the antenna. A fixed arm 58 may mechanically couple the coaxial waveguide 30" to the inner cone 26". An additional cyclic movement is also employed, however, because the inner structure is constructed to have an eccentrically varying axis of rotation. The central co-axial waveguide 30 which serves as an axial support member is provided with an offset portion 60, on the further side of which from the conical transmission line it is journalled in a fixed bearing 61. The slightly offset portion 60 of the coaxial waveguide is spun eccentrically about the central axis by a rocker arm 62 from a source of reciprocating motion 63. This eccentric spinning movement is at a higher speed than the rotation of the inner cone.

As may be seen in FIG. 7 the central axis of the inner cone is in this arrangement angularly shifted a selected amount about the apex with respect to the outer cone 24". The drive mechanism 56, 57 and the central coaxial line 30 are, however, concentric with respect to the outer cone 24". Thus as the inner structure is rotated by the drive motor (not shown) it moves eccentrically with respect to the outer cone 24".

The continuous rotation and the eccentric spinning of the inner assembly therefore provides the desired continuous conical scanning action. Control of the beam displacement from the central longitudinal axis is principally achieved by selection of the slow wave propagation and the aperture 2 spacing in accordance with considerations given above. Control of the circumferential position of the beam about the axis is achieved by the rotational position of the inner structure with respect to the outer cone 24". Consequently, a major nutating pattern results which causes scanning in space. Because of the eccentric spinning of the axis of rotation by the rocker arm 62, there is a lesser movement of the beam which provides the desired conical scanning.

It will be understood that conical scanning action may also be provided by other forms of drive mechanism or slow wave structure. Thus the dielectric structure between the inner and outer cones may be eccentrically positioned, with the inner and outer cones being substantially concentric with respect to each other. Or, an eccentric drive mechanism may be employed to wobble an inner structure which is physically symmetrical in shape to the outer cone. The high speed eccentric spinning could be provided as in FIG. 7 or by other means. Both types of structures provide the desired conical transmission line mode of propagation and the slow wave form of propagation which is utilized for scanning control.

Thus there has been provided an improved scanning antenna particularly suitable as a fiush mounted nose cone antenna for high speed aircraft. The antenna provides a pencil beam which can be scanned with any type of raster, throughout a forward conical volume. The antenna is capable of conical lobing around the direction of beam point. The antenna uses a structure which further occupies a relatively small volume and is of light weight.

I claim:

1. An antenna array for scanning with respect to a given axis and comprising in combination a conical waveguide structure having an inner cone movable with respect to the outer cone, the outer cone being apertured with radiating slots; and dielectric wave slowing means positioned in the space between the cones of the conical Waveguide for selectively slowing propagation of energy therein in dependence upon the relative positions of the cones of the conical waveguide.

2. An antenna comprising: a conical transmission line having an apex and an apertured outer surface; wave energy feed means coupled to said conical transmission line at said apex; and slow wave means disposed within said conical transmission line asymmetrically about the axis of said line whereby said slow wave means will have different angular positions about said apex relative to said conical transmission line.

3. An antenna comprising: a conical transmission line having inner and outer conductors, the inner conductor being movable about its central axis relative to the axis of the outer conductor and the outer conductor including radiation apertures; means for exciting the conical transmission line at the apex thereof with microwave energy, and means positioned between the conductors of the conical transmission line for selectively slowing wave energy therein dependent upon the relative positions of the condoctors, such that the phase of excitation of the apertures in the outer cone are selectively determined, the spacing of the apertures along the axis being selected 8 with respect to the amount of slowing so that a single radiated beam is provided.

4. An antenna including the combination of a transmission line extending along a given axis, the transmission. line extending from an apex and having a radially expanding cross section in a plane transverse to the axis, the cross section being in the general form of a circle and the outer surface of the transmission line being apertured; means for feeding energy to the apex of the transmission line so that wave energy is propagated in three-dimensional fashion from the apex along the axis and about the circle; a dielectric member positioned in the inner space of the transmission line and only partially filling the space, the dielectric extending circularly about the transmission line; and means for varying the position of the dielectric member within the transmission line, so that wave energy propagated along the transmission line is effectively slowed to an extent determined by the proportion of dielectric present in the space extending along the transmission line from the apex.

5. A scanning antenna comprising: an outer conductive shell having the form of a surface of revolution about a given axis and an apex on the axis, the outer conductive shell having radiating apertures therein; an inner conductive shell within the outer conductive shell and of like configuration, there being a spacing between the outer surface of the inner shell and the inner surface of the outer shell; means for cyclically varying the relative positions of the two shells so that the inner shell may be displaced angularly with respect to the outer shell; means for feeding microwave energy to the apex of the inner and outer shells so that energy is propagated along the shells in the space between the shells; and means fixed to at least one of the shells in the space between the shells for slowing the velocity of propagation of wave energy therein.

6. An antenna comprising: an outer conductive cone having a number of radiating slots; an inner conductive cone forming a conical transmission line with the outer cone and angularly movable with respect thereto; means for feeding microwave energy to the apex of the cone transmission line; and means including a dielectric structure positioned between the conductive cones for selectively slowing energy in the conical transmission line in spatial dependence upon the relative positions of the conductive cones, the radiating apertures in the outer cone being spaced with respect to the slowed energy such that a reverse end-fire beam having an instantaneous position dependent upon the relative cone positions is provided.

7. An antenna for scanning about a given axis and comprising: a conical transmission line having its apex pointed in the general direction desired for scanning and having an outer conductor symmetrical with the given axis and an inner conductor with an axis which can be moved in all directions with respect to the given axis; means for cyclically nutating the position of the inner conductor with respect to the outer conductor; a dielectric con-e positioned between the outer conductor and the inner conductor and symmetrically disposed with respect to the axis, the radial dimension of the dielectric cone being less than the angular spacing between the conductors, so that as the inner conductor is nutated the speed of propagation of energy within the conical transmission line is slowed to a greater extent along a line which rotates about the conical transmission line and about its apex; and the outer conductor containing a plurality of radiating apertures having a lengthwise spacing along the axis which provides a unidirectional radiation pattern only when the conductors are in close relation, the radiation pattern being a reverse end-fire characteristic and thus provided in the desired direction along the selected axis.

8. A forward scanning antenna comprising: an outer conductive cone having a plurality of radiating apertures therein, the cone being symmetrical with a central axis and the spacing of the apertures along the axis being selected to be substantially less than a waveguide wavelength, the cone being suitable for mounting with the apex directed in a forward scanning direction; a first inner dielectric cone having an outer surface con-forming to and supporting the outer conductive cone and an inner surface symmetrical with the longitudinal axis; a second dielectric cone positioned within and being substantially like the first dielectric cone but of smaller conical angle; an inner conductive cone within the internal portion of the second dielectric cone, the outer and inner conductive cones providing a conical waveguide structure and the first and second dielectric cones providing a variable wave slowing structure which propagates electromagnetic Wave energy at a speed slower than the speed of light and dependent upon the spacing between the outer surface of the second dielectric cone and the inner surface of the first dielectric cone; means coupled to the inner conductive cone and the second dielectric cone for scanning the beam by moving the inner conductive cone with respect to the longitudinal axis of the structure, so that the spacing between the dielectric cones varies to cause beam scanning; and wave energy feed means mounted within the inner conductive cone and extending through the apex thereof to introduce wave energy in a conical waveguide mode into the space between the first and second dielectric cones, the apertures being positioned so that beam collimation is achieved with selected polarization.

9. An antenna comprising: a conical transmission line defined by outer and inner conductive cones, the outer cone being apertured and the inner cone tapering from a maximum cross section to a smaller cross section at its base; a layer of low-loss dielectric disposed on the inner conductive cone and providing a slow wave structure; wave energy feed means coupled to the apex of the conical transmission line; and a wave energy dissipation structure comprising a plurality of resistive vanes at the base of the conical transmission line and disposed in the space between the outer conductive cone and the smaller cross section of the inner conductive cone.

10. A conical scanning antenna comprising: an outer conductive cone having a plurality of radiating apertures therein, the cone being symmetrical with a central axis; an inner conductive cone within the outer cone and forming therewith a conical transmission line; at least one dielectric cone interposed between the inner and outer conductive cones; means mounting the inner cone with its central axis at an angle with respect to the outer cone; means coupled to the inner cone for rotating the inner conductive cone principally about the central axis of the outer cone to provide an eccentric movement with respect thereto; means coupled to the means for rotating for concurrently providing an additional eccentric movement of the axis of rotation of the inner conductive cone; and means coupled to the conical transmission line for feeding wave energy to the apex thereof.

11. A conical scanning antenna comprising: a conical transmission line including outer and inner conductive cones, the outer cone being apertured; dielectric means interposed between the conductive cones and providing therewith an angular air gap within the conical transmission line which varies circumferentially about the conical transmission line; means coupled to the inner cone to rotate said inner cone circumferentially with respect to the outer cone, thus changing the relative position of the air gap; means coupled to the inner cone for eccentrically shifting the axis of rotation thereof, to provide a conical scanning movement; and means for feeding wave energy to the conical transmission line.

12. A unidirectional antenna comprising a conical ransrnission line disposed symmetrically about the axis thereof and having an apex located on said axis, the outer surface of said transmission line having a plurality of apertures through which electromagnetic energy may be radiated, wave energy feed means coupled to said conical transmission line for supplying said electromagnetic energy thereto, slow wave means disposed within said conical transmission line asymmetrically about said axis whereby said energy radiated from said apertures will be radiated predominantly in some predetermined direction.

References Cited in the file of this patent UNITED STATES PATENTS 2,433,924 Riblet Ian. 6, 1948 

